The following coefficients must be defined for each improper type via the improper_coeff command as in the example above, or in the data file or restart files read by the read_data or read_restart commands:
· K (energy/radian^2)
· X0 (degrees)
X0 is specified in degrees, but LAMMPS converts it to radians internally; hence the units of K are in energy/radian^2.
Should not K be just energy? The cos function is dimensionless, so therefore, cos^2 will be as well.
Could that be a transcription error from copying something over from a quartic dihedral or harmonic angle potential web page where the form is K*angle^2?
Thanks.
–Fred
The following coefficients must be defined for each improper type via the
*improper_coeff* <http://lammps.sandia.gov/doc/improper_coeff.html> command
as in the example above, or in the data file or restart files read by the
*read_data* <http://lammps.sandia.gov/doc/read_data.html> or
*read_restart* <http://lammps.sandia.gov/doc/read_restart.html> commands:
· K (energy/radian^2)
· X0 (degrees)
X0 is specified in degrees, but LAMMPS converts it to radians internally;
hence the units of K are in energy/radian^2.
Should not K be just energy? The cos function is dimensionless, so
therefore, cos^2 will be as well.
Could that be a transcription error from copying something over from a
quartic dihedral or harmonic angle potential web page where the form is
K*angle^2?
yes, that is very likely the cause. in fact, a quick search through the
documentation sources with grep reveals, that this applies to several other
styles using the cosine of an angle as well. i'll be updating the
documentation sources and it should be included in the next release.
axel.